The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Historically both ABS (antilock braking system) and TCS (traction control system) implemented in cars and trucks started with the goal of addressing two fundamental tasks: 1) preventing excessive wheel slip for stability and steerability of the vehicle; and 2) maximizing the vehicle acceleration/deceleration potential to meet the operator's driving requirements. (The rest of the disclosure will refer to acceleration/deceleration simply as acceleration with the understanding that acceleration is a mathematical quantity with signs.) Over time many ABS/TCS systems have evolved to include additional requirements in addition to these tasks. For example, when an electronic stability control (ESC) system activates, a wheel may need to be controlled to a large slip target to momentarily cause a reduction in lateral force generated by that particular wheel. Another example, during split μ ABS (where “μ” is the coefficient of friction between the vehicle's tires and the road surface), the high μ wheel's braking force must increase in a controlled manner when trying to maximize the vehicle deceleration.
Conventionally, the controllable quantities from available actuators on the vehicle are 1) brake torque for each wheel; and 2) engine torque for the driven axle of the vehicle. These quantities combine to affect the wheel dynamics and vehicle acceleration in a complicated and non-linear manner. For situations involving the ABS system, the effect of the engine can be neglected in most cases, making this mechanism easier to analyze and control. In TCS situations, the engine is always a significant factor, and this complication is unavoidable.
Traditionally it has often been difficult to simultaneously accomplish both the task of wheel slip control and the task of vehicle acceleration control in their respective desirable ways, especially for TCS (because of the above discussed complication).